netdev - Re: [PATCH bpf v2 1/3] bpf_redirect_neigh: Support supplying the nexthop as a helper parameter

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Date:   Tue, 20 Oct 2020 20:08:21 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf v2 1/3] bpf_redirect_neigh: Support supplying the
 nexthop as a helper parameter

Daniel Borkmann <daniel@...earbox.net> writes:

> On 10/20/20 12:51 PM, Toke Høiland-Jørgensen wrote:
>> From: Toke Høiland-Jørgensen <toke@...hat.com>
> [...]
>>   BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
>> @@ -2455,8 +2487,8 @@ int skb_do_redirect(struct sk_buff *skb)
>>   		return -EAGAIN;
>>   	}
>>   	return flags & BPF_F_NEIGH ?
>> -	       __bpf_redirect_neigh(skb, dev) :
>> -	       __bpf_redirect(skb, dev, flags);
>> +		__bpf_redirect_neigh(skb, dev, flags & BPF_F_NEXTHOP ? &ri->nh : NULL) :
>> +		__bpf_redirect(skb, dev, flags);
>>   out_drop:
>>   	kfree_skb(skb);
>>   	return -EINVAL;
>> @@ -2504,16 +2536,25 @@ static const struct bpf_func_proto bpf_redirect_peer_proto = {
>>   	.arg2_type      = ARG_ANYTHING,
>>   };
>>   
>> -BPF_CALL_2(bpf_redirect_neigh, u32, ifindex, u64, flags)
>> +BPF_CALL_4(bpf_redirect_neigh, u32, ifindex, struct bpf_redir_neigh *, params,
>> +	   int, plen, u64, flags)
>>   {
>>   	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>>   
>> -	if (unlikely(flags))
>> +	if (unlikely((plen && plen < sizeof(*params)) || flags))
>> +		return TC_ACT_SHOT;
>> +
>> +	if (unlikely(plen && (params->unused[0] || params->unused[1] ||
>> +			      params->unused[2])))
>
> small nit: maybe fold this into the prior check that already tests non-zero plen
>
> if (unlikely((plen && (plen < sizeof(*params) ||
>                         (params->unused[0] | params->unused[1] |
>                          params->unused[2]))) || flags))
>          return TC_ACT_SHOT;

Well that was my first thought as well, but I thought it was uglier.
Isn't the compiler smart enough to make those two equivalent?

Anyway, given Jakub's comment, I guess this is moot anyway, as we should
just get rid of the member, no?

-Toke